【Unity】ComputeShaderの基本的な使い方についてまとめる

#pragma kernel HeavyProcess

RWStructuredBuffer<int> intBuffer;
int intValue;

[numthreads(64,1,1)]
void HeavyProcess(uint3 groupID : SV_GroupID, uint3 groupThreadID : SV_GroupThreadID)
{
    intBuffer[groupThreadID.x] = 0;
    for (int i = 0; i < 100; i++)
    {
        intBuffer[groupThreadID.x] += intValue;
    }
}

using UnityEngine;

public class HeavyProcess : MonoBehaviour
{
    [SerializeField] private ComputeShader computeShader;
    private int _kernelHeavyProcess;
    private ComputeBuffer _intComputeBuffer;

    private void Start()
    {
        // カーネル取得
        _kernelHeavyProcess = computeShader.FindKernel("HeavyProcess");

        // Buffer領域を確保
        _intComputeBuffer = new ComputeBuffer(64, sizeof(int));

        // パラメータの設定
        computeShader.SetInt("intValue", 1);
        computeShader.SetBuffer(_kernelHeavyProcess, "intBuffer", _intComputeBuffer);
    }

    private void Update()
    {
        // GroupIDを指定して数回実行
        // (64,1,1)スレッド * (1,1,1)グループ
        computeShader.Dispatch(_kernelHeavyProcess, 1, 1, 1);

        // 実行結果
        var result = new int[64];
        _intComputeBuffer.GetData(result);
        Debug.Log("RESULT: HeavyProcess");
        for (var i = 0; i < 64; i++)
        {
            Debug.Log(i + ":　" + result[i]);
        }
    }

    private void OnDestroy()
    {
        // バッファの解放
        _intComputeBuffer.Release();
    }
}

#pragma kernel DrawTexture

RWTexture2D<float4> textureBuffer;

// SV_DispatchThreadID: あるカーネルを実行するスレッドが全てのスレッドのどこに位置するか
// SV_Group_ID * numthreads + GroupThreadID
[numthreads(8,8,1)]
void DrawTexture(uint3 dispatchThreadID : SV_DispatchThreadID)
{
    // X方向になるほど濃くなるようにする
    float width, height;
    textureBuffer.GetDimensions(width, height);
    textureBuffer[dispatchThreadID.xy] = float4(
        dispatchThreadID.x / width,
        dispatchThreadID.x / width,
        dispatchThreadID.x / width,
        1);
}

using UnityEngine;

public class DrawTexture : MonoBehaviour
{
    [SerializeField] private ComputeShader computeShader;
    [SerializeField] private Renderer planeRenderer;

    private int _kernelDrawTexture;
    private RenderTexture _renderTexture;

    private struct ThreadSize
    {
        public readonly int X;
        public readonly int Y;
        public readonly int Z;
        public ThreadSize(uint x, uint y, uint z)
        {
            X = (int) x;
            Y = (int) y;
            Z = (int) z;
        }
    }
    private ThreadSize _kernelThreadSize;

    private void Start()
    {
        // RenderTextureの生成
        _renderTexture = new RenderTexture(512, 512, 0, RenderTextureFormat.ARGB32);
        _renderTexture.enableRandomWrite = true;
        _renderTexture.Create();

        // カーネル取得
        _kernelDrawTexture = computeShader.FindKernel("DrawTexture");

        // スレッドサイズの取得
        computeShader.GetKernelThreadGroupSizes(_kernelDrawTexture,
            out var threadSizeX,
            out var threadSizeY,
            out var threadSizeZ);
        _kernelThreadSize = new ThreadSize(threadSizeX, threadSizeY, threadSizeZ);

        // テクスチャの設定
        computeShader.SetTexture(_kernelDrawTexture, "textureBuffer", _renderTexture);

        // カーネルの実行
        // 水平方向のグループ数: 512 / 8 = 64
        // それぞれのスレッドで設定する範囲を分担する
        computeShader.Dispatch(
            _kernelDrawTexture,
            _renderTexture.width / _kernelThreadSize.X,
            _renderTexture.height / _kernelThreadSize.Y,
            _kernelThreadSize.Z);

        // テクスチャの設定
        planeRenderer.material.mainTexture = _renderTexture;
    }
}